1. Technical Field
The present invention relates to semiconductor devices and a method for manufacturing the same.
2. Related Art
Conventionally, fluorescent display tubes (Vacuum Fluorescence Display: VFD) are used as a display device in home electric appliances on-vehicle instruments and the like. This fluorescent display tube carries out display operation with an electrooptic effect similar to that of CRT (Cathode Ray Tube). While a high voltage of, for example, 10K volt is required for the display operation of CRT, a voltage of, for example, several tens of volts. is required for the display operation of fluorescent display tubes.
Incidentally, miniaturization of semiconductor devices has progressed, and the chip area has been reduced, thus contributing to realize further lower power dissipation. On the other hand, the break down voltage level of semiconductor devices is decreasing. In realizing driver devices for the fluorescent display tube by means of semiconductor devices, for example, 60 volt is required as the break down voltage level of the semiconductor devices. In the semiconductor devices of such a high break down voltage, the transistor size, the wiring space, and the like need to be increased, thereby preventing the reduction of the chip area.
Especially, in the driver device for the fluorescent display tube, a plurality of driver circuits for electrodes at the anode side of the fluorescent display tube are disposed. Since there are limitations in reducing the size of the driver transistors of a high break down voltage, the disposed length of a plurality of driver circuits has become long in the driver devices used for fluorescent display tubes, and thus a capability of disposing each driver circuit with a narrow pitch is strongly demanded.
Japanese Unexamined Patent Publication No. 6-45602 is an example of the related art.
Japanese Unexamined Patent Publication No. 2001-196546 is another example of the related art.
Incidentally, the driver circuit of the driver device used for fluorescent display tubes can be configured using driver transistors. When disposing such a driver circuit along the disposing direction of the electrodes at the anode side of the fluorescent display tube, it is conceivable that the source region of the driver transistors configuring the driver circuit is disposed so as to share the source region of the adjoining driver transistor (in the driver circuit). In this case, the length in the disposing direction can be reduced because the source region is shared.
On the other hand, in the semiconductor devices disclosed in the examples of the related art, techniques to reduce each driver transistor while maintaining a high break down voltage are disclosed. Accordingly, even if multiple disposition is carried out by using such driver transistors and by causing them to simply share the source region, the break down voltage level may not be increased.
In general, in case of sharing a source region, for the purpose of stabilizing the substrate potential it is necessary to provide a back gate electrode in the source region, the back gate electrode for giving a relevant substrate potential. For this reason, even if driver transistors of a high break down voltage are simply disposed, it may not be possible to supply or to take out electric charges sufficiently to/from the substrate via the back gate electrode. Accordingly, as the voltage increases, it will be impossible to function as a transistor and thus the so-called breakdown voltage will be reduced.